Patent GB-507993-A (GB)
Title: Improvements in rate of change of pressure responsive instruments such as rate of climb indicators for aircraft
IPC: G01P3/62
Filed: 1937-09-17
Abstract: 507,993. Pressure gauges. BENDIX AVIATION CORPORATION. Sept. 17. 1937, No. 25331. Convention date, March 6. [Class 106 (ii)] Relates to a rate of change of pressure responsive instrument such as a rate of climb indicator for aircraft wherein means are provided to equalize the pressure within and without a pressure responsive element, and comprises a plurality of gas flow retarding elements and associated therewith means responsive to variations of temperature and/or pressure of the surrounding gas for varying the restriction to gas flow. In a synthetic resin casing 9 is a frame formed by front and back plates 11, 10 connected by distance pieces 12 which supports a capsule 14 in communication with the outside atmosphere and indicating mechanism. Movement of the capsule in response to pressure changes is transferred by rod 30, pivoted arm 37, pin and shaft 44, and quadrant and pinion 47, 50 to a pointer 51. The zero of the instrument may be adjusted from outside by turning a button 100 which through gears 101, 102 moves a stud 18 axially which bears on the end of a flexible strip 17 carrying the capsule. The latter communicates with the space inside the casing 9 by pipes 24, 26 coupling 27 and a capillary assembly 62, 75, 95. The coupling 27 is connected by a pipe 60 to a thermally insulated or vacuum bottle chamber 61. Flange 58 connects to a dehumidifier (not shown) whereby air at static atmospheric pressure enters the casing 9. Also connected to the coupling 27 is the capillary assembly 62 whereby air from within the capsule 14 is allowed to escape in a regulated manner. The vacuum bottle 67 is centred in a shell 61b by a spring 61c. The pipe 60 is connected to a conduit 64 passing through the base 65 to which is connected a base 70 on which is mounted an evacuated bellows 71 the volume of which varies with the outside pressure thus varying the effective volume of air in the reservoir. The capillary structure is mounted on base 72 seated hard against packing 72c by the pull on a threaded sleeve 72a. Openings 72d lead to chamber 73. Leading from this chamber by a connection 74 is a capillary tube 75 coiled at 75a and leading to a chamber 76. Screwed into this is a fitting 77 containing a valve 81 normally urged from its seat 82 by a spring 86. A bi-metallic strip 87 presses on the valve spindle 80. Leading from chamber 76 is a second capillary 95 coiled at 95a and exhausting into the casing 9 at 96. Operation. At sea-level air at normal pressure enters the casing-9 and flows through openings 97 and valve 81 to chamber 76 and by capillary 75 to chamber 73 or enters capillary 95 at 96 and flows to chamber 76 and then by capillary 75 to chamber 73, according to the temperature and setting of strip 87. Then. air flows froin chamber 73 to parts 27 and by pipes 26 and 24 to capsule 14. If the same altitude is maintained the pressure inside and outside the capsule 14 equalizes and the pointer 51 indicates zero. Upon increase of altitude, the casing pressure falls and air escapes from the chamber 14. If the air temperature is at the lower limit for which strip 87 is set the valve 81 is closed and cold air flowing more freely than warmer, both capillaries 95 and 75 are in circuit. If temperature is at the high limit, the valve is open and capillary 95 is byepassed. Specification 507,991 is referred to.